Proliferated, bisporangiate, and other atypical cones occurring on young, plantation-grown Larix laricina

Abstract

Atypical cones were found in 1983 and 1984 on many trees in three young plantations of Larix laricina (Du Roi) K. Koch. On-shoot and within-crown locations of cones of each type were noted as the cones were collected, at the stage of anthesis or receptivity, for analysis by dissection or sectioning. Development of other cones of each type was monitored. Proliferated seed cones had more bracts than typical seed cones and were commonly located where more vigorous vegetative development (neoformation) was likely. Most bisporangiate cones had proximal microsporophylls and distal bracts; a few also had microsporophylls at their apices. The bisporangiate cones were subdivided according to proportions of different appendages. Those with more female appendages tended to occur on short-shoot axes more distally located along the parent long shoot and thus where more vigorous development was likely. Bisporangiate cones with mainly female appendages developed to seed-cone maturity. Those with mainly male appendages died soon after anthesis. Pollen cones usually have no basal foliage leaves, but some pollen cones with such leaves occurred. The leaves died with the cone tissues after anthesis. Occurrence, composition, and development of these atypical cones were discussed in relation to their position, shoot vigour, and preformation.

Sexual stability in the nearly dioeciousPinus johannis(Pinaceae)

“…Environmental changes have been shown to induce sexual changes in angiosperms and gymnosperms species with genetically determined dioecious sexual systems in angiosperms (Freeman et al, 1980; Stelkens and Wedekind, 2010). In conifers, changes in sexual expression can be induced experimentally, including the production of bisporangiate strobili, by application of exogenous hormones (Tosh and Powell, 1986; Owens and Hardev, 1990; Wakushima et al, 1997). Changes in hormone levels can be caused by environmental factors such as light intensity (Alabadí and Blázquez, 2009).…”

Abnormal Cones in Cupressus Sempervirens

“…Natural occurrence of bisexual cones is commonly the outcome of an unknown environmentalsetting (see review by Tosh and Powell 1986), but in Pinus monticola (Bingham et al 1969), and Larix laricina (Du Roi) K. Koch (Tosh and Powell1986), some trees form bisexual cones regularly, and this seems to indicate a genetic basis (Bingham et al 1969;Tosh and Powell 1986).…”

3. Control of sex expression in conifers

“…Although the reproductive structures of conifers are normally unisporangiate, bisporangiate and proliferated strobili occasionally occur in nearly all species (11,48,86,94,121,137) . These range from mainly vegetative ( Fig.…”

“…Female>male and male>vegetative transformations also occur but more rarely . Such transformations may occur spontaneously as a more or less normal event in young trees entering sexual maturity (11,137), but more commonly in response to promotive stresses (3,25), pruning (48) and PGR treatments (48,69,94 ; S.D . Ross and R .F.…”